prolongation vs lengthening

prolongation and lengthening both are nouns.

Word	Noun	Adjective	Verb	Adverb
prolongation	Yes	No	No	No
lengthening	Yes	No	No	No

As nouns, prolongation and lengthening are synonyms defined as:

Other synonyms of prolongation include perpetuation, protraction.

prolongation (noun)	lengthening (noun)
the act of prolonging something	the act of prolonging something
amount or degree or range to which something extends
the consequence of being lengthened in duration